Aristeidis Noutsos

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Aristeidis Noutsos University of Manchester
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Scattering Effects on Rotation Measure
High sensitivities and broad bandwidths of
current instruments allow us accurate
determination of the interstellar Faraday
Rotation. LOFAR will have the advantage of low
frequencies, where this effect is strong.
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Scattering Effects on Rotation Measure
Simulations by Karastergiou (2009) showed that
scattering can produce phase-resolved RM
variations across the pulse profile. Each RM
across the pulse could be fitted well with a
?2-law.
These effects are evident even for small
scattering time-scales (tscat 2 ms).
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Observational Evidence
We calculated phase-resolved RM profiles for the
19 strongest, highly polarised pulsars in Noutsos
et al. (2008).
In 9 cases we saw significant RM variations
across the profile e.g.
?(RM) 13 rad m2
?(RM) 37 rad m2
?(RM) 52 rad m2
RM
PA
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Summary Discussion

• We have detected significant RM variations, as a
  function of pulse phase, for 9 highly polarised
  pulsars observed with the Parkes telescope, at 20
  cm.

• We have detected significant RM variations, as a
  function of pulse phase, for 9 highly polarised
  pulsars observed with the Parkes telescope, at 20
  cm.

• The possibility that this is caused by
  frequency-dependent quasi-orthogonal emission
  modes was ruled out.

• The possibility that this is caused by
  frequency-dependent quasi-orthogonal emission
  modes was ruled out.

• Generalised Faraday Rotation was deemed unlikely,
  but may still play a role. The theory of GFR
  gives little information on the magnitude of its
  effect.

• Generalised Faraday Rotation was deemed unlikely,
  but may still play a role. The theory of GFR
  gives little information on the magnitude of its
  effect.

• Scattering on polarization has been studied by Li
  Han (2003) and more recently by Karastergiou
  (2009). We have found a good correlation between
  scattering and the amount of RM variation, which
  makes this explanation simple and appealing.

• Scattering on polarization has been studied by Li
  Han (2003) and more recently by Karastergiou
  (2009). We have found a good correlation between
  scattering and the amount of RM variation, which
  makes this explanation simple and appealing.

• Future studies should account for this effect. RM
  determination from only a few, high-s/n bins can
  lead to erroneous estimates, and averaging may be
  required (but beware of depolarization!).

• Future studies should account for this effect. RM
  determination from only a few, high-s/n bins can
  lead to erroneous estimates, and averaging may be
  required (but beware of depolarization!).